Embodiments of the present invention generally relate to processes and apparatuses for the integration of a blast furnace and an air separation unit to increase production of the blast furnace.
For purposes of this patent, the following terms are defined. As used herein, the term xe2x80x9cair separating unitxe2x80x9d or xe2x80x9cair separation unitxe2x80x9d means and refers to a facility, plant, location or process for separating the components of air and may include both cryogenic and non-cryogenic facilities. As used herein, the terms xe2x80x9cenhance,xe2x80x9d xe2x80x9cenhanced,xe2x80x9d and/or xe2x80x9cenhancing,xe2x80x9d means and refers to an act of altering and/or changing. As used herein, the term xe2x80x9coxygen supplyxe2x80x9d means and refers to an oxygen supply with a determinable oxygen content and is not limited nor excluded from a pure supply, but rather, may be any concentration of oxygen and/or oxygen content. As used herein, the term xe2x80x9coxygen richxe2x80x9d and xe2x80x9coxygen rich streamxe2x80x9d means and refers to a gas or gases having an oxygen content greater than about 21.0% by volume. As used herein, the term xe2x80x9cblast furnace airxe2x80x9d or xe2x80x9cblast furnace feed gasxe2x80x9d means and refers to feed to a blast furnace to enable reduction of ores, blast furnace feed gas is not limited to one feed supply and may, in some cases, incorporate several sources of feed. As used herein, the term xe2x80x9cnitrogen richxe2x80x9d and xe2x80x9cnitrogen rich streamxe2x80x9d means and refers to a gas or gases having an nitrogen content greater than about 80% by volume.
As well, the use of a particular structure, structures, or embodiments is not meant to be limiting. For instance, the term xe2x80x9capparatusxe2x80x9d or xe2x80x9capparatusesxe2x80x9d means and includes production facilities, plants, and the like. Further, the term xe2x80x9cprocessxe2x80x9d or xe2x80x9cprocessesxe2x80x9d means and includes xe2x80x9cmethods,xe2x80x9d xe2x80x9cplans,xe2x80x9d xe2x80x9cproduction plans,xe2x80x9d and the like. The term xe2x80x9cled out,xe2x80x9d xe2x80x9cfed,xe2x80x9d xe2x80x9cfeeding,xe2x80x9d and xe2x80x9cfeedxe2x80x9d means and refers to allowing out, passing out, discharging, releasing, and/or the like.
Air separation plants are common in the art. Typical air separation units comprise at least one column in which components of air are separated into an oxygen rich liquid and a nitrogen rich gas. Feed gas, such as air, rising in the column is brought into gas-liquid contact in a countercurrent state with a reflux liquid flowing down from above. As a result, the downward liquid flow is gradually enriched in components whose boiling points are higher than that of nitrogen to become an oxygen rich liquid. In the same manner, upward rising vapor is gradually enriched in nitrogen to become a nitrogen rich gas. The degree of separation can be controlled by numerous factors, such as, but not limited to, the number of trays, height of column, number of columns, point of extraction of product, conditions of separation, and the like.
Blast furnaces are common in the art and primarily used for extraction of metals from ores, or the removal of oxygen from a metal oxide to produce the metal. A process of this type is commonly referred to as smelting. There are many different structures and types of blast furnaces available for smelting and each one may differ for its particular use or particular metal to produce.
There are many methods of operation of a blast furnace. Typical methods of operation of a blast furnace entail loading the blast furnace with a charge. The charge typically, but not in all cases, includes a quantity of ore, coke and a flux such as limestone. The charge is loaded into an upper portion of the blast furnace. At the same time, a gas, usually air, is introduced into the blast furnace. Oxygen is necessary in the feed gas for proper functioning of the blast furnace. The oxygen allows, as the feed gas passes through the charge, for a portion of the charge to be oxidized to carbon dioxide or carbon monoxide. The carbon monoxide then reduces the ore and reverts to carbon dioxide.
The use of oxygen rich gas, such as air, in a blast furnace is desirable for at least the following reasons: (1) with the use of an oxygen enrichment it is possible to switch to powdered charcoal and/or other fuels and to reduce coke consumption in the blast furnace and (2) with the use of an oxygen enrichment, production of the blast furnace may be increased. Accordingly, as the prior art has illustrated, various attempts have been made to facilitate the use of oxygen enrichment. A prior art example of a modification to a blast furnace is described in U.S. Pat. No. 5,244,489. In this patent, an oxygen plant equipped with a mixing column can efficiently treat a portion of blast furnace air to produce oxygen, which is injected into the blast air stream to yield the enriched feed gas. This allows for reducing the mass flow of oxygen-contained gas sent to the furnaces for the reduction of iron ore. More air can therefore be added to the furnace to increase the output of the steel production without increasing the system pressure drop.
Other prior art integrations are disclosed in U.S. Pat. Nos. 5,268,019 and 5,295,351. These patents describe various possible configurations for integrating an air separation unit with a gas turbine operated with low-BTU gas produced by a blast furnace. Air is extracted from the gas turbine to feed the air separation process. Low-BTU gas is compressed and heat exchanged with the extracted air before feeding the combustion chamber of the gas turbine. In a variant, the fuel is saturated with moisture prior to the expansion step to further increase turbine output.
Another similar patent is U.S. Pat. No. 5,317,862. This patent describes a similar configuration as U.S. Pat. Nos. 5,268,019 and 5,295,351. However, in this patent, the nitrogen stream from the air separation unit is heated, saturated with moisture and expanded to recover energy.
Other examples exist in the prior art for the treatment of a blast furnace, but do not combine various beneficial synergies of an air separation unit and a blast furnace. For example, another prior art example is found in U.S. Pat. No. 5,582,036. This patent describes the possibility of using a double-re-boiler type oxygen plant for blast furnace operation. Another prior art patent is U.S. Pat. No. 6,045,602. This patent describes the integration of the air separation unit and the subsequent gas treatment system to produce hydrogen gas to be used in the direct reduction of iron ore.
These prior art examples are beneficial, however, further advantages may be realized. For example, it would be advantageous for steel making companies to be able to increase production of a blast furnace without having to invest in new and/or high cost facilities. Additionally, it would be advantageous to efficiently utilize a blast furnace to maximize a return on investment and/or a more complete utilization of a process gas. As well, it would be advantageous to incorporate at least a portion of the aforementioned improvements while not appreciably increasing a cost of operating a blast furnace. Accordingly, the art field is in search of methods and apparatuses that may achieve at least a portion of these benefits.
Generally processes and apparatuses of the present invention relate to the integration of an air separation unit and a blast furnace. In embodiments of the present invention, at least a portion of a blast furnace feed gas may be removed and separated in an air separation unit, whereby an oxygen rich stream produced from the air separation unit may be fed to the blast furnace feed gas to enrich the oxygen content of the feed gas to the blast furnace, thereby increasing production of the blast furnace. Additionally, a second stream removed from the air separation unit may be expanded for recovery of energy. Further embodiments utilize a portion of the blast furnace off gas for the recovery of power.
This summary is not intended to be a limitation with respect to the features of the invention as claimed and any examples are merely intended as embodiments, and the scope and other objects can be more readily observed and understood in the detailed description and the claims that follow.